Ben,
I take it that you are reusing the old tops on Coopers plastic bottles?
I got a pack of new tops trom Big Dub for a few $$$ & had no trouble at all.
Off topic I know, but can anyone remember the thread where someone explained how to use Google to operate the forum Search Function?
:beer:
I used new lids, some just didn't work...
search like this (for example)... Youngs Double Chocolate Stout site:aussiehomebrewer.com
It's a pain in the backside typing the site bit everytime but it works much better...